Isolated DC-DC Converter Issue

Thread Starter

circuits9

Joined Feb 2, 2020
18
Good afternoon: My circuit requires an isolated power supply. I have settled on a Murata 3.3V input to 3.3v output isolated dc-dc converter. The input voltage is measured close to 3.3v and am expecting 3.3v from dc-dc converter. However, when I check the voltage on the output, it is about 4.7v when the spec sheets show an output of 3.3v. I have tried two different brands of converters and they perform the same way. What am I missing? Below is a link to the datasheet of the one I am currently testing. Any guidance would be much appreciated!!

https://www.digikey.com/products/en?keywords=811-2747-ND

https://www.murata.com/products/productdata/8807029669918/kdc-mee1.pdf?1583754812000
 

crutschow

Joined Mar 14, 2008
29,504
I don't offhand seen it mentioned but some regulators require a minimum load for proper regulation.
Try a 100 ohm to 1k ohm load and see if that makes a difference.
 

Thread Starter

circuits9

Joined Feb 2, 2020
18
I don't offhand seen it mentioned but some regulators require a minimum load for proper regulation.
Try a 100 ohm to 1k ohm load and see if that makes a difference.
Hey,
A 100ohm results in 4.56V. A 1K results in 4.55V. I confirmed input is 3.286V. Any more ideas?
 

Thread Starter

circuits9

Joined Feb 2, 2020
18
I am connecting the positive lead from the multimeter to the V+ on the isolated side with a resistor and the negative lead of the V- on the isolated side.
 

Thread Starter

circuits9

Joined Feb 2, 2020
18
100 Ohms was enough. Now it shows 3.5v. I didn't have the 100ohm resistor connected right the first time I tried it. Thanks again for the help!
 

Thread Starter

circuits9

Joined Feb 2, 2020
18
Good morning,
Wanted to get you guys opinion: My application requires I get isolated power and ground to a 555 timer with a resistive sensor which is why I was attempting to use an isolated power supply. The issue is that my circuit doesn't draw enough load to trigger the regulation function on the isolated DC-DC converter. I would have to keep an 100-200 ohm resistor in place to generate enough load to regulate the output voltage. Is that acceptable or do you think it would be better to just go with an unregulated isolated DC-DC converter and put in a LDO voltage regulator? Thanks again for your help.
 

Thread Starter

circuits9

Joined Feb 2, 2020
18
Well, the other issue I have is even with the added resistor, I still get an output of 3.5V. Is there a reason it can't output a clean 3.3V?
 
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